U.S. patent application number 11/792500 was filed with the patent office on 2008-05-22 for method and materials for improving evaporative heat exchangers.
This patent application is currently assigned to FF SEELEY NOMINEES PTY LTD. Invention is credited to Robert Wilton James.
Application Number | 20080116592 11/792500 |
Document ID | / |
Family ID | 36677299 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080116592 |
Kind Code |
A1 |
James; Robert Wilton |
May 22, 2008 |
Method and Materials for Improving Evaporative Heat Exchangers
Abstract
A corrugated laminate material (44) for use in an evaporative
heat exchanger, said material including a water retaining medium
having a wettable surface (40) and an opposed vapour resistant
surface (42).
Inventors: |
James; Robert Wilton; (South
Australia, AU) |
Correspondence
Address: |
TAROLLI, SUNDHEIM, COVELL & TUMMINO L.L.P.
1300 EAST NINTH STREET, SUITE 1700
CLEVEVLAND
OH
44114
US
|
Assignee: |
FF SEELEY NOMINEES PTY LTD
St. Mary's
AU
|
Family ID: |
36677299 |
Appl. No.: |
11/792500 |
Filed: |
January 4, 2006 |
PCT Filed: |
January 4, 2006 |
PCT NO: |
PCT/AU06/00025 |
371 Date: |
June 6, 2007 |
Current U.S.
Class: |
261/23.1 ;
156/196; 156/60; 165/60; 261/101; 261/127; 264/286; 427/299 |
Current CPC
Class: |
B32B 29/08 20130101;
F24F 5/0035 20130101; B32B 2250/02 20130101; Y02B 30/545 20130101;
Y10T 156/10 20150115; F28D 5/02 20130101; Y02B 30/54 20130101; B32B
2255/12 20130101; B32B 2307/7246 20130101; F28F 25/087 20130101;
B32B 3/28 20130101; B32B 29/06 20130101; Y10T 156/1002 20150115;
B32B 25/10 20130101; F24F 1/0007 20130101; B32B 2307/7265 20130101;
B32B 2307/554 20130101; B32B 2597/00 20130101 |
Class at
Publication: |
261/23.1 ;
261/101; 156/60; 261/127; 264/286; 156/196; 427/299; 165/60 |
International
Class: |
B32B 3/28 20060101
B32B003/28; F28F 25/00 20060101 F28F025/00; F24F 6/00 20060101
F24F006/00; F24F 3/14 20060101 F24F003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2005 |
AU |
2005900235 |
Claims
1. A corrugated laminate material for use in an evaporative heat
exchanger, said corrugated laminate material including a water
retaining medium having a wettable surface and an opposed vapour
resistant surface.
2. The corrugated laminate material as claimed in claim 1, wherein
the corrugations are equi-sized.
3. The corrugated laminate material as claimed in claim 1, wherein
the corrugations are mutually parallel at a common angle across the
length of at least a portion of said corrugated laminate
material.
4. The corrugated laminate material as claimed in claim 1, wherein
the corrugations are at varying angles across the length of at
least a portion of said corrugated laminate material.
5. The corrugated laminate material as claimed in claim 1, wherein
the water retaining medium is selected from treated wettable paper,
moulded paper fibre slurry, wettable particulate sintered polymers
and metallic or polymer films having treated or modified surfaces
to promote wetting.
6. The corrugated laminate material as claimed in claim 1 wherein
the vapour resistant surface is formed from a plastic film liquid
polymer or vapour resistant treatment applied to one surface of the
water retaining medium.
7. A method of making a corrugated laminate material for use in an
evaporative heat exchanger comprising the steps of: providing a
planar sheet of water retaining medium; and forming corrugations by
the planar sheet of water retaining medium through corrugating
rollers.
8. The method as claimed in claim 7, further comprising the step of
applying a vapour resistant surface during formation of the
corrugations.
9. The method as claimed in claim 7, further comprising the step of
applying a vapour resistant surface before or after formation of
the corrugations.
10. The method as claimed in claim 8, further comprising the step
of applying the vapour resistant surface by hot calendaring it onto
or adhering it to the planar sheet while the planar sheet is being
fed through the rollers.
11. The method as claimed in claim 9, further comprising the step
of spraying the vapour resistant surface onto the planar sheet.
12. A heat exchange element for a core for use in an evaporative
heat exchanger formed from at least one sheet of corrugated
laminate material, wherein the at least one sheet of corrugated
laminate material having first and second sides, said first side
includes a water retaining medium having a wettable media and a
said second side includes a vapour resistant surface, the
corrugated laminated material being folded to form at least fold
such that the interior of each fold forms a wettable surface
passage or a vapour resistant channel.
13. The heat exchange element of claim 12, further comprising a
plurality of elements wherein each element includes said sheet and
where the respective sheet in said plurality of elements are placed
side by side in a substantially parallel relationship such that
adjacent surfaces of each sheet form a wettable surface passage or
a vapour resistant passage.
14. The heat exchange element of claim 12, formed from at least two
of said sheets of corrugated laminate material, wherein the two
sheets are joined to form a passage having corrugated walls for
airflow therethrough and wherein the corrugations on opposite sides
of the passage are at intersecting angles.
15. The heat exchange element as claimed in claim 14, wherein the
passage is bounded by vapour resistant surfaces.
16. The heat exchange core including a plurality of heat exchange
elements as claimed in claim 14 stacked side by side such that
passages between the stacked elements provide wettable surface
passages.
17. A method of making a heat exchange core comprising the steps
of: providing a plurality of pairs of sheets of corrugated laminate
material each sheet having first and second sides, said first side
includes a water retaining medium having a wettable media and a
said second side includes a vapour resistant surface; spacing said
plurality of pairs of sheets in a substantially parallel spaced
apart relationship; forming a plurality of pockets from pairs of
said sheets where the inner surfaces of each pocket are vapour
resistant surfaces; sealing adjacent edges of each pair of
substantially parallel spaced apart sheets together to form
open-ended pockets; and stacking said pockets in a substantially
parallel relationship to form wettable surface airflow passages
between each pair of adjacent pockets.
18. A method of effecting heat exchange between counter current
airflows in a heat exchanger comprising the steps of: providing a
heat exchange core within the heat exchanger comprising wet and dry
airflow channels in counter flow; and forming said wet and dry
airflow channels with corrugated walls; wherein entry air is passed
down the dry airflow channels to exit as conditioned air, a portion
of the exit air being reversed to pass through the wet channels and
effect heat exchange between the dry and wet airflow channels
before being exhausted.
19. (canceled)
20. A method of operating an evaporative cooler comprising the
steps of: providing a heat exchange core having adjacent wet and
dry airflow channels; orienting said wet and dry airflow channels
to counter current airflow heat exchange relationship; supplying
water to the wet channels in a descending flow pattern; supplying
water to the wet channels over a plurality of segments from an air
entry end to an air outlet end of said heat exchange core during
operation of said evaporative cooler; and circulating water through
each segment relatively separately from adjacent segments such that
an appropriate temperature gradient is established from an air
inlet end to an air outlet end of the core by maintaining different
circulating water temperatures in each segment.
21. A method of operating an evaporative cooler comprising the
steps of: providing a heat exchange core adapted for heat exchange
airflow therethrough via a plurality of heat exchange channels, at
least some of said channels being wet channels; applying water to a
wettable material in the wet channels, the wettable material
retaining the water; applying water to the wet channels in an
intermittently and generally uniformly descending flow pattern
across the entire core; and repeating the application of water to
the wet channels of the core before the wettable material has dried
out.
22. The method as claimed in claim 20, wherein the step of
providing the heat exchange core includes a heat exchange core
comprising a plurality of elements wherein each element includes a
sheet having first and second sides, said first side includes a
water retaining medium having a wettable media and a said second
side includes a vapour resistant surface and where the respective
sheet in said plurality of elements are placed side by side in
parallel such that adjacent surfaces of each sheet form a wettable
surface passage or a vapour resistant passage.
23. An evaporative cooler including a heat exchange core
comprising: a plurality of elements wherein each element includes a
sheet of corrugated laminate material having first and second
sides, said first side includes a water retaining medium having a
wettable media and a said second side includes a vapour resistant
surface; the respective sheet in each of said plurality of elements
are placed side by side in a substantially parallel relationship
such that adjacent surfaces of each sheet form a wettable surface
passage or a vapour resistant passage; a water distribution system
including a plurality of water distributors for wetting the
wettable surfaces, passages, or channels, said water distributors
being positioned above the core and disposed in spaced apart
parallel relation transversely of the core relative to an airflow
direction through the core, each water distributor being located
within a respective space above the core separate from adjacent
water distributor spaces, each water distributor being supplied
from a respective reservoir, and further including flow restriction
means at an airflow exit of the vapour resistant channels for
effecting counter flow of a portion of the exit air through the wet
channels to an exhaust.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to improvements in heat
exchange capacity of evaporative heat exchangers. In particular,
one aspect of this invention relates to a material suited to use in
forming heat exchange surfaces of evaporative heat exchangers.
Additional inventions are disclosed that relate to the operation of
evaporative coolers. For ease of understanding, the aspects of this
invention will be described in connection with the heat exchange
core of counter flow evaporative coolers, as well as to methods,
equipment and systems for the ventilation and cooling of enclosed
spaces. The various aspects of this invention can be applied to
self-contained air conditioning units suitable for supplying cooled
air to an enclosed space, and to self-contained conditioning units
suitable for supplying cooled water for use in heat exchange units
forming part of a system for the cooling of enclosed spaces.
DESCRIPTION OF THE PRIOR ART
[0002] Throughout this description and the claims which follow,
unless the context requires otherwise, the word "comprise`, or
variations such as "comprises" or "comprising", will be understood
to imply the inclusion of a stated integer or step or group of
integers or steps.
[0003] The reference to any prior art in this specification is not,
and should not be taken as, an acknowledgement or any form of
suggestion that that prior art forms part of the common general
knowledge in Australia.
[0004] The use of evaporative air coolers for the cooling of
enclosed spaces is well known in the art. These coolers are
typically constructed with outer walls containing a wettable,
permeable media, which is kept wet with water pumped from an
internal reservoir. Air from outside the building is drawn through
the wetted media by means of a fan located within the evaporative
cooler, and delivered either directly into the enclosed space or
through a system of ducting to the enclosed space.
[0005] As air passes through the wetted media, a phenomenon known
as adiabatic saturation takes place. Moisture from the surfaces of
the wetted pad evaporates into the air passing through in
accordance with the humidity of the air, or its ability to take up
additional water vapour. This evaporation causes an exchange of
energy wherein the energy required for liquid water to evaporate to
a vapour is derived from the water within the wetted pad, thereby
cooling the water. The warm air entering the pad is then cooled by
heat exchange to the cool water surface. The limit to which air can
be cooled by this phenomenon is known as the Wet Bulb Temperature
as defined in any reference work on psychrometrics.
[0006] The air delivered by an evaporative cooler is cooled to a
temperature which is always greater than the Wet Bulb Temperature,
to a degree determined by the efficiency of the design of the
evaporative cooler. The air delivered is also always more humid
than the air entering the cooler. This limitation in achievable
temperature and the addition of moisture to the air severely limits
the degree of cooling available by this method, as well as limiting
the use of this means of cooling to relatively hot, dry climates.
In a typically hot, dry location, such as Adelaide, Australia, the
design condition for evaporative cooling is 38.degree. C. Dry Bulb
Temperature, 21.degree. C. Wet Bulb Temperature. Under these design
conditions, a typical evaporative air cooler will deliver air at
around 23.5.degree. C., but which has been substantially
humidified. This air is much less amenable to providing comfort
conditions within the enclosed space than, say, a refrigeratively
cooled air conditioning system, which might deliver air at
15.degree. C., and to which no additional moisture has been
added.
[0007] There is also known, in the prior art methods, that air can
be cooled to temperatures below the Wet Bulb Temperature of the
incoming air while still using only the evaporation of water as the
mechanism of cooling. These methods typically pre-cool the incoming
air without the addition of moisture by means of dry heat exchange,
prior to the air coming in contact with the moist surfaces for
evaporation. The pre-cooling of air without addition of moisture
reduces both the Dry Bulb and Wet Bulb temperatures of the air as
can be observed on any psychrometric chart. When the air is then
brought into contact with the wetted surfaces, it will be cooled to
a temperature which approaches the now depressed Wet Bulb
Temperature rather than the original Wet Bulb Temperature. If this
process is taken to the limit, it is possible to produce cooled air
which approaches the Dew Point of the incoming air, without the
addition of moisture.
[0008] This process of indirect evaporative cooling of air is well
known. SU 979796 by Maisotsenko discloses a configuration wherein a
main stream of air is passed along a dry duct, simultaneously
passing an auxiliary air stream counter currently along a moist
duct which is in heat-exchange relation with the dry duct. The
auxiliary stream is obtained by subdividing the total stream into
main and auxiliary streams.
[0009] This configuration is further developed by Maisotsenko in
U.S. Pat. No. 4,977,753 wherein the wet and dry ducts are divided
into two separate sections which allows for pre-cooling of the dry
airstreams prior to their entry into the wet duct thereby resulting
in enhanced cooling efficiency.
[0010] A practical implementation and method of construction of the
configuration of U.S. Pat. No. 4,977,753 is disclosed in U.S. Pat.
No. 5,301,518 by Morozov et al. U.S. Pat. No. 5,301,518 discloses a
construction consisting of alternating dry ducts, which may be
constructed from a variety of materials, and wet ducts constructed
from capillary porous material. The airflow configuration is
arranged such that the air streams in the dry and wet ducts are in
counter flow as in previous disclosures. Furthermore, the
configuration divides the heat exchanger into two separate stages
for the purpose of achieving the requisite temperature reduction
while relieving the high pressure drop inherent in the narrow air
passages required for adequate heat transfer. Wetting of the porous
material of the wet ducts is achieved by vertical wicking from a
water reservoir beneath the heat exchanger.
[0011] The disclosure of U.S. Pat. No. 5,301,518 has been
demonstrated in practical working machines, which produce air
cooled to temperatures approaching the Dew Point without the
addition of moisture to the air. However, the construction suffers
a number of deficiencies. Resistance to air flow is high as a
result of the narrow air passages needed for effective heat
transfer. Heat transfer between the wet and dry air passages is
inefficient due to the air boundary layers at both sides of the
medium between the passages, requiring large surface areas for
effective transfer of heat. The heat exchanger height is limited by
the ability of the porous wet duct material to wick vertically,
which in practical terms is about 200 mm. The available delivered
airflow for a given size of heat exchanger is therefore low,
resulting in an unacceptably large and costly construction for
practical airflows. There are also considerable practical
difficulties with the construction and operation of such an
indirect evaporative cooler. Manifolding of air streams to the
respective wet and dry ducts requires individual separation of the
ducts with laborious and expensive sealing systems. When used with
normal potable water supplies, water evaporated from the wet duct
leaves behind salts, which cannot be easily removed, eventually
clogging the heat exchanger.
[0012] It is also well known that heat exchange and wet surface
evaporation rates from flat, plane surfaces can be greatly enhanced
by arranging adjacent surfaces in the form of corrugations set at
different angles for each adjacent sheet. This principle was
disclosed by Bredberg in U.S. Pat. No. 3,262,682 and Norback in
U.S. Pat. No. 3,395,903 for the construction of evaporative media
for use in evaporative air coolers and cooling towers. The
interaction of air streams within the adjacent corrugations in this
construction of wetted media results in intense evaporation from
the wet surfaces and intense heat transfer from the cold surfaces
formed as a result of that evaporation. A compact, high efficiency
evaporative media can be constructed with minimal pressure loss
from airflow.
[0013] The intensity of evaporation and heat exchange demonstrated
in corrugated evaporative media would greatly enhance the
performance of an indirect evaporative cooler if applied to the
airflow configuration needed for indirect cooling if such media
could be readily adapted to that environment.
SUMMARY OF THE INVENTION
[0014] A first aspect of the present invention provides a
corrugated material for use in an evaporative heat exchanger, said
material including a water retaining wettable surface and an
opposed vapour resistant surface.
[0015] In a preferred embodiment, the shape of the corrugated
pattern within the sheets may be varied to optimise thermal
performance and airflow resistance when the corrugated material is
used in a heat exchange core.
[0016] In a second aspect the present invention provides a method
of making a corrugated laminate material as described herein,
wherein a planar sheet of a water retaining medium is shaped with
corrugations by being fed through corrugating rollers.
[0017] In a third aspect the present invention provides a heat
exchange core for an evaporative heat exchanger formed from at
least one sheet of corrugated material as described herein, wherein
the at least one sheet is folded to form at least one pocket or
fold such that the interior of each fold forms a wettable surface
passage or channel or a vapour resistant passage or channel.
[0018] In a fourth aspect the present invention provides a heat
exchange element for a core of an evaporative heat exchanger, said
element being formed from at least two sheets of corrugated
laminate material as described herein, wherein the two sheets are
joined to form a passage having corrugated walls for airflow
therethrough and wherein the corrugations on opposite sides of the
passage are at intersecting angles.
[0019] In a preferred embodiment, the angle of intersection of the
corrugations of adjacent corrugated sheets is varied so as to
optimise thermal performance and airflow resistance of the heat
exchange core.
[0020] A preferred indirect evaporative heat exchanger core is
characterised by a construction consisting of individual corrugated
wettable media sheets modified to include a vapour impermeable
barrier on one side. The individual sheets are constructed into
open pockets sealed top and bottom with the vapour impermeable
barrier on the inside of the pocket. Said pockets are then
assembled into a stack of pockets by sealing each of the non vapour
barrier sides together at the air entry end of the stack of pockets
such that a complete core is formed wherein warm, dry air enters
the core through the pockets, passing all the way through the
pockets. Upon exit from the pockets, a proportion of the air so
delivered is returned through passages formed between the wettable
non-vapour barrier sides of adjacent pockets, which form wet
passages of the core.
[0021] In a fifth aspect the present invention provides a method of
making a heat exchange core comprising taking a plurality of pairs
of sheets of corrugated laminate material as described herein,
forming a plurality of pockets from pairs of said sheets where the
inner surfaces of each pocket are vapour resistant surfaces,
adjacent edges of each pair of parallel spaced apart sides being
sealed together to form open-ended pockets and stacking said
pockets in parallel to form wettable surface airflow passages
between each pair of adjacent pockets.
[0022] In a sixth aspect the present invention provides an
evaporative cooler including a heat exchange core formed from at
least one sheet of corrugated laminate material as described
herein, wherein the at least one sheet is folded to form at least
one pocket or fold such that the interior of each fold forms a
wettable surface passage or channel or a vapour resistant passage
or channel.
[0023] In a seventh aspect the present invention provides a method
of effecting heat exchange between counter current airflows in a
heat exchanger, said heat exchanger including a heat exchange core
comprising wet and dry airflow channels in counter flow, said
channels being formed with corrugated walls and wherein entry air
is passed down the dry channels to exit as conditioned air, a
portion of the exit air being reversed to pass through the wet
channels and effect heat exchange between the dry and wet channels
before being exhausted.
[0024] In relation to a further aspect of the present invention, it
is a severe deficiency in prior art indirect evaporative coolers
that water must be placed within the wettable media by wicking.
This requirement comes about due to the temperature gradient
through the wet passage necessary for the cooler to work. The
wetted surfaces at the delivery end of the core must be close to
the Dew Point of the incoming air if the delivered air temperature
is to approach the Dew Point, whereas the wetted surface
temperature at the entry end of the core must approach the
temperature of the incoming hot dry air if evaporation and heat
transfer are to occur. Thus there must be a temperature gradient in
the wetted surfaces through the core from the delivery end to the
entry end. This gradient can only be achieved by wicking water from
a reservoir to the point where it is to evaporate in prior art
arrangements. Any surplus of water over this requirement to
evaporate and keep the surfaces wet will degrade thermal
performance and it will no longer be possible to approach the Dew
Point in delivered air temperature. If the wetted surfaces were to
be flood irrigated as is the practice with direct evaporative
cooling, it would only be possible for the delivered air
temperature to approach the Wet Bulb temperature of the incoming
air. This temperature can be considerably above the Dew Point
depending on incoming air psychrometrics.
[0025] In an eighth aspect of the present invention there is
provided a method of operating an evaporative cooler which includes
a heat exchange core wherein adjacent wet and dry airflow channels
are in counter current airflow heat exchange relationship with
water being supplied to the wet channels in a descending flow
pattern, characterised in that water is supplied to the wet
channels over a plurality of segments from an air entry end to an
air outlet end of said core during operation of said cooler and
wherein water is circulated through each segment relatively
separately from adjacent segments such that an appropriate
temperature gradient is established from an air inlet end to an air
outlet end of the core by maintaining different circulating water
temperatures in each segment.
[0026] Preferably, the method of the eighth aspect is further
characterised by the delivery of water through each water
distributor from a respective pumping means associated with each
water reservoir.
[0027] In a further embodiment, the water reservoirs are each
connected to a common water conduit such that water levels in each
reservoir are allowed to reach an equilibrium level.
[0028] In a ninth aspect the present invention provides a method of
operating an evaporative cooler which includes a heat exchange core
adapted for heat exchange airflow therethrough via a plurality of
heat exchange channels, at least some of said channels being wet
channels with water being applied to and retained by wettable
material in the wet channels, characterised in that water is
applied to the wet channels in an intermittently and generally
uniformly descending flow pattern across the entire core and
wherein the application of water to the wet channels of the core is
repeated before the wettable material has dried out.
[0029] In a preferred embodiment, a single pumping means, water
spreader and reservoir applies water to the evaporative core
periodically.
[0030] In a tenth aspect the present invention provides an
evaporative cooler including a heat exchange core as described
herein having corrugated wet and dry passages or channels, a water
distribution system including a plurality of water distributors for
wetting the wettable surfaces of the passages or channels, said
water distributors being positioned above the core and disposed in
spaced apart parallel relation transversely of the core relative to
an airflow direction through the core, each water distributor being
located within a respective space above the core separate from
adjacent water distributor spaces, each water distributor being
supplied from a respective reservoir, and further including flow
restriction means at an airflow exit of the vapour resistant
channels for effecting counter flow of a portion of the exit air
through the wet channels to an exhaust.
[0031] The inventive aspects of the present invention when combined
can result in an indirect evaporative cooler which fully utilises
the characteristics of corrugated media to produce a compact,
efficient and economical cooler. Such an indirect evaporative air
cooler typically comprises a fan means for the delivery of air, an
indirect evaporative heat exchanger and an air delivery means
including an airflow resistance means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Embodiments of aspects of the present invention will now be
described by way of example with reference to the accompanying
drawings, in which:
[0033] FIG. 1 is an isometric view of the construction of a prior
art corrugated evaporative media;
[0034] FIG. 2 shows schematic views of airflow paths and a water
distribution method of a prior art indirect evaporative cooler;
[0035] FIG. 3 is a sectional view of a dry channel showing the
construction of an embodiment of corrugated media in accordance
with the invention;
[0036] FIG. 4 shows a sectional view and schematic of a segment of
an indirect evaporative cooler core made from the corrugated media
of FIG. 3;
[0037] FIG. 5 is an isometric view, which shows an embodiment of
the construction of a pocket segment of an indirect evaporative
cooler core employing corrugated media of the present
invention;
[0038] FIG. 6 is an isometric view of an assembly of pocket
segments of FIG. 5 when formed into an indirect evaporative cooler
core;
[0039] FIG. 7 is a schematic showing the water distribution system
of another aspect of the present invention where the heat exchange
core is divided into segments; and
[0040] FIG. 8 is an isometric view of an assembled indirect
evaporative cooler core detailing water and airflow systems.
DESCRIPTION OF EMBODIMENTS
[0041] In FIG. 1, the prior art corrugated media is shown as a
block of sheets of corrugated, wettable media within which dry air
and water on the wetted surfaces interact. The block 1 is
constructed from individual sheets 4 of corrugated media (typically
treated paper of a type which readily wicks water along its
surface). Individual corrugations 6 are impressed in the media
during manufacture and the sheets arranged such that the
corrugations are set at an angle 8 to the edges of the block of
media. Adjacent sheets 4 are typically glued together with reversed
corrugation angles creating complex air and water passages within
the matrix of the block.
[0042] In operation, water is introduced in the direction 3 and
applied to the top surface of the block of media. As the water 3
descends through the matrix, it encounters numerous points within
the matrix where the corrugations 6 of adjacent sheets 4 meet. At
each of these intersection points, part of the water is directed
one way around the intersection, and the remainder of the water the
opposite way around the intersection. Since there are numerous such
intersections within the matrix, the water is quickly spread evenly
throughout the block of media, thereby ensuring even wetting of the
surfaces. The distribution of water within the matrix is further
enhanced by the property of the media to readily wick water along
its surface. Thus any deficiencies in the evenness of water
distribution throughout the surfaces of the matrix are readily
compensated and corrected.
[0043] Hot, dry air 5 enters the matrix and also encounters
numerous intersections of the adjacent corrugated sheets. At each
intersection, the air is divided into two streams ensuring uniform
movement of air throughout the matrix. At each of these
intersections there is intense interaction between the air and the
wetted surfaces due to the rapid and frequent changes in direction
of the airflow. This intense interaction results in rapid
evaporation of water from the wetted surfaces, thereby humidifying
the air and cooling the waters on the wetted surfaces. Since the
wetted surfaces are then considerably cooler than the hot dry
incoming air, heat exchange will then occur between the air and the
wetted surface, thereby cooling the air. Air leaves the matrix
block as cooled, humidified air 7. The heat exchange during this
process is also intensified due to the numerous interaction sites
at the intersections of corrugations for the same reasons as for
intensified evaporation espoused above.
[0044] In FIG. 2, a prior art indirect evaporative cooler
construction is shown. Hot, dry air 10 enters the dry air passage
12, proceeding past the dry air passage boundary 14. When the
construction has been operating for at least a short period, the
dry air passage boundary 14 will be cooler than the dry air
entering the passage 12. Heat exchange will occur and the dry air
will be progressively cooled as it proceeds down the dry air
passage.
[0045] The incoming hot dry air 10 has been cooled considerably
when it leaves the dry air passage 14 at 15. A flow resistance
device 28 is installed in the airflow path thereby causing an
increase in air pressure at 15. This increase in pressure causes
some of the now cool, dry air to turn at 26, and proceed through
the wet air passage 16. The wet air passage contains a wetted media
18, kept moist by the wicking of water from a water reservoir 22.
Since the air has not yet had any change in its moisture content,
evaporation takes place from the wetted media 18 thereby
humidifying the air and cooling the water within the wetted media
by the same mechanism described above for evaporative media. As the
air continues its flow down the wet passage, heat from the adjacent
dry passage 12 will tend to raise the temperature of the now
moistened air 26, thereby increasing its ability to evaporate
moisture further. Further evaporation and heating takes place until
the air 26 reaches a barrier in its path at 20, causing it to flow
to exhaust 21.
[0046] Air which flows through the flow resistance 28 becomes the
delivered air 24. This air has been cooled without the addition of
moisture. In the limit of low airflows and good heat exchange, the
temperature of delivered air 24 can approach the Dew Point of the
incoming air.
[0047] FIG. 3 shows an element of the construction of the current
invention. A corrugated wettable media 40 (which may be made using
similar materials and manufacturing methods to that of individual
sheets 4 of the evaporative media described above) is manufactured
with a vapour resistant membrane 42 adhered to one side. The
membrane 42 may be a polymer material, although the only essential
property is that it resist the flow of water vapour. It may be
applied by a number of methods, including hot calendaring of
plastic, adhering plastic film or the application of liquid
polymers (e.g. paint), or it may be formed by treatment of the
surface of the wettable media. The vapour membrane should be kept
as thin as practicable for maximum heat transfer. The wettable
media 40 should also be as thin as practicable consistent with its
requirement to keep the surface wet and wick water to areas not
directly wetted in the constructed cooler.
[0048] In the construction described above, the wettable media 40
from which the core elements 44 are made can be manufactured from
any material which can be readily wetted. Practical materials
include treated, wettable paper, moulded paper fibre slurry,
wettable particulate sintered polymers and metallic or polymer
films with treated or modified surfaces to promote wetting. Those
skilled in the art will be aware of other wettable materials which
may be used in the construction of the current invention.
[0049] Further, the core elements 44 may be produced using a
moulding process wherein the shape of the corrugated passages may
be modified to further facilitate the optimisation of airflow and
heat transfer. In particular, the air passages through which
exhaust air leaves the core may be shaped to reduce the airflow
pressure losses associated with turning the air within the core
from the general flow direction to a general exhaust direction.
[0050] FIG. 4 shows the component part described in FIG. 3 as part
of the heat exchanger and evaporation core of the indirect
evaporative cooler, the current invention. In the complete
construction, dry, hot airflows through the dry air passage 50,
where the dry air passage is contained between the vapour resistant
surfaces 42 of the corrugated sheets 44. Adjacent wet passages 52
are formed between the wettable media surfaces 40. Airflows through
the dry passages 50 in general counter flow to the wet passages
52.
[0051] The angle at which corrugations are set to the general
direction of airflow is illustrated by the angle 54. This angle may
be varied over a wide range to optimise the efficiency of heat
transfer and resistance to airflow in the core. In general, a
shallower angle 54 will result in lower airflow resistance at the
penalty of reduced heat transfer efficiency.
[0052] In another embodiment, the angle of corrugation 54 within
the core is made relatively shallow, typically in the range 20
degrees to 35 degrees. The shallow angles of corrugation
significantly reduce the airflow resistance through the core to the
detriment of heat transfer efficiency. Heat transfer efficiency can
be regained by extending the overall length of the core. It is
found that within the range of angles stated herein, an optimised
combination of reduced airflow resistance and increased core length
can be achieved for each construction, consistent with adequate
heat transfer efficiency.
[0053] FIG. 5 shows the detail of construction of the components
described in FIG. 4 to achieve the flow patterns and directions
required. Individual pockets 88 are constructed from two corrugated
sheets with vapour resistant membranes 44. Each corrugated sheet 44
is positioned with the vapour resistant membrane 42 facing the
vapour resistant membrane of the adjacent sheet. The sheets are
sealed together at the top seal 84 and bottom seal 86, thus forming
a complete pocket with all inner surfaces lined with a vapour
resistant membrane 42. The top seal 84 and bottom seal 86 can be
formed by methods including clinching, adhesives, plastics welding
or fillers. Alternatively, if the vapour resistant membrane is
formed from plastic film adhered to the wettable media 40, one of
either the top seal or bottom seal can be formed by folding of a
double size sheet of media and membrane combination.
[0054] This construction results in a sealed lined pocket through
which hot dry air can flow with no physical contact with the
wettable media in passage 80.
[0055] FIG. 6 shows the stacking of several of the pockets 88
formed into an indirect cooler core 94. When successive pockets are
placed in a stack adjacent to each other, adjacent wettable media
surfaces then form the wet passage 82. Air flowing through the wet
passage 82 has no physical contact with the dry passage 80, but
heat exchange between the wet and dry passages and evaporation
within the wet passage can readily take place with the intensity
promoted by the corrugated construction.
[0056] Adjacent pockets 88 need to have the wet passages 82
separated from the dry passages 80 at the end of the core through
which hot, dry air enters the core. This is achieved by sealing
together adjacent pockets on the wettable media side with a seal
line 90 formed by similar methods to the seals at the top and
bottom of the pockets (84 and 86). With this construction, hot, dry
air entering from 92 can only enter and flow through the pockets 88
lined with vapour resistant membranes 42, and must travel all the
way through the pocket until it exits at the opposite end 96.
[0057] FIG. 7 shows an arrangement in accordance with an embodiment
of the eighth aspect of the present invention for wetting of the
wettable media in the wet passages in a segmented manner.
[0058] The arrangement of FIG. 1 divides the core 94 into a number
of segments 62 (shown as five segments in FIG. 7, but a lesser or
greater number of segments could be used). Each segment has its own
pumping means 60, its own water reservoir 66 and its own water
distribution system 68. The segment 62 of core 94 with its
corrugated construction, tends to pass water from the water
distributor 68, through the core 94 to the water reservoir 66 with
little mixing of water from adjacent segments. Since, in operation,
all segments are circulating water simultaneously, any tendency of
the circulating water in a segment to pass through to an adjacent
segment is approximately balanced by an equal and opposite tendency
for water to come back from that adjacent segment. Thus, for each
segment water is circulated relatively independently of each of the
adjacent segments. The circulating water temperature in each of the
segments can therefore be different, thus providing the temperature
gradient necessary to thermal performance of the indirect
evaporative cooler, and thus allow the delivered air temperature to
approach the Dew Point. This arrangement for water supply to the
core has several advantages over the prior art, including removal
of the restriction on core height due to the wicking capability of
the wettable media; water flow surplus to the requirement for
evaporation flushes away any salt concentration due to evaporation
and water quality can be easily monitored for salt concentration
and diluted before critical concentrations are reached.
[0059] This arrangement would approach the ideal wetting condition
of wicking if there were many segments. Thermal performance is
compromised if there are too few segments. In practice it has been
found that dividing the core into 4-6 segments gives thermal
performance approaching a wicking system with a considerably more
robust and enduring core for practical applications.
[0060] In practical examples, it has been found that water
descending through the core does not remain in separated segments
as in the ideal case. There is, in practice, some drift of water
between the segments resulting in the accumulation of water in some
segment water reservoirs, and a deficiency of water in other
segments. This practical difficulty is overcome by the provision of
a bypass conduit 70 between the reservoirs, where the bypass
conduit 70 is connected to each of the segment water reservoirs via
an opening 72. Should the surplus/deficiency problem of water
descending through the core arise, water level variations in the
reservoirs 66 will equalise through the conduit 70 until a steady
state of flow between the reservoirs is established. This
arrangement also allows for water filling at one reservoir only, by
allowing water levels to again equalise according to the steady
state requirements of the individual segments.
[0061] In an alternative arrangement in accordance with the ninth
aspect of the present invention, the segmented water distribution
system of FIG. 7 is replaced with a single, general uniform means
of distributing water over the entire core, a single water pump
means, and a single water reservoir at the bottom of the core 94.
In this embodiment, water is applied to the core intermittently.
The single water pump 60 is operated for a short period of time
sufficient to uniformly wet all of the internal surfaces of the
core, and is then turned off. The indirect evaporative cooler is
then continued in operation, cooling by means of evaporation of the
water contained on its internal surfaces. Since there is no further
flow of water through the wetted surfaces of the core during this
phase of operation, the wetted surfaces will cool to temperatures
similar to the temperatures of an indirect evaporative core wetted
by means of wicking as in the prior art. The requirements of
thermal gradient within the wetted passages are met, and thermal
performance of the core is not significantly degraded. The wetting
operation by means of the pump 60 is repeated before the wetted
surfaces of the core are dried out, resulting in some degradation
of thermal performance during the wetting phase. Typically, with
the selection of wettable media materials with reasonable water
holding capacity, the core can be wetted in 30-60 seconds, and the
indirect cooler operated without further wetting for 15-20 minutes
without the wetted surfaces in the core drying out
significantly.
[0062] FIG. 8 shows the complete core 94 with the water
distribution system 68 and the airflow system 104 in place. Each
water distributor is located within a space 101 kept separate from
the water distributor space of adjacent segments by barriers 100.
The sealed spaces 101 and barriers 100 are necessary to prevent
airflow exiting from the wet passages of the core thereby causing
air in the wet passages to travel all the way along the wet
passages. A similar sealing system is necessary to separate the
water reservoir 66 from adjacent water reservoirs. Each water
reservoir 66 is sealed to the core by barriers 102 thus preventing
any air from leaving the wet passages through the water
reservoirs.
[0063] Immediately after the entry end of the core, the wet passage
space is left open at 106. The opening 106 allows the now moist,
warn air flowing in the wet passages to exhaust from the core 94.
In the preferred embodiment, an exhaust opening 106 is provided at
both the top and bottom of the core although only the top opening
is shown in FIG. 8. However, if provision of the opening 106 at the
bottom of the core is impracticable, satisfactory performance can
still be achieved with only the opening 106 at the top with some
degradation of thermal performance.
[0064] The ratio of delivered air to exhaust air is adjusted by
means of a flow restriction 108 in the delivered air stream.
Closing flow restriction 108 increases the pressure in chamber 109
at the delivery end of the core 94, thereby increasing the flow of
air back through the wet air passages.
* * * * *